The density of the image in a color photographic emulsion layer is the result of the amount of color photographic coupler which has reacted or coupled with oxidized photographic developer to form a dye. Given a class of color couplers, the conventional way of increasing the dye density for a fixed amount of light exposure has been to increase the amount of photographic silver halide or coupler or by increasing the amount of silver halide in the layer per unit of surface area, or to reduce the size of the silver halide grains or combinations of these techniques. By increasing the amount of silver halide or coupler in an emulsion layer, however, the cost of that emulsion layer is also increased significantly.
U.S. Pat. No. 4,207,393 found that certain phenolic materials were useful in the enhancement of contrast for silver halide photographic emulsions. These materials were particularly effective in photographic layers containing magenta couplers.
It has been found in the practice of the present invention that the addition of a certain class of phenolic compounds, different from those disclosed in U.S. Pat. No. 4,207,393, to a color photographic emulsion layer changes the shape of the conventional D (optical density) vs log E (energy of exposure) curve so as to desirably change the contrast of the emulsion. The effect of these phenolic compounds is to increase the density of the dye image formed at a given exposure level without necessarily changing the ratio of silver to coupler. In fact, one can maintain a given image dye density at a fixed exposure with reduced amounts of silver halide in the presence of enhancers of the present invention. In addition, the effect of these compounds is apparently somewhat different than that of increasing the amount of coupler or silver, in that the portion of the D-log E curve affected by these compounds is different than for changes affected by altering the silver to coupler ratio. The use of these compounds affects the upper portion or the shoulder of the D-log E curve as well as the curve shape. These enhancers are particularly useful with magenta couplers of the 1-phenyl-3-anilino-5-pyrazolone class.